In a conventional semiconductor device, a barrier metal is often deposited on the inner walls of holes such as contact holes or via holes. A metal material is then formed on the barrier metal to thereby fill the holes. TaSiN is considered to be the best material for use as the barrier metal, but a drawback of TaSiN is that its resistivity is too high.
The TaSiN barrier is typically formed by PVD (physical vapor deposition) or CVD (chemical vapor deposition). In PVD, a TaSi target is reacted with nitrogen while undergoing physical vaporization to thereby realize the deposition of TaSiN. The advantage of PVD is that manufacture is made easy. However, when TaSiN is used as a barrier metal for copper metal lines, Cu3Si is formed on the interfacial surfaces of the TaSiN and Cu because copper is easily diffused while in a polycrystalline state. Further, with the use of PVD, it is difficult to obtain a step coverage of a desired level in a device requiring a high aspect ratio.
As a result of the problems associated with PVD, more resources are being directed toward research into using CVD to form TaSiN. U.S. Pat. Nos. 6,376,371 and 6,436,825 are examples of conventional CVD methods for forming TaSiN.
However, because of various organic residual materials present in a precursor used in CVD, the deposited TaSiN has a high resistivity. When TaSiN having a high resistivity is used as a barrier metal for copper metal lines, the overall resistance of the device is increased. This results in deterioration of metal line reliability.